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Effect of water temperature shifting on mortality of Japanese flounder Paralichthys olivaceus experimentally infected with viral hemorrhagic septicemia virus
- Sano, Motohiko, Ito, Takafumi, Matsuyama, Tomomasa, Nakayasu, Chihaya, Kurita, Jun
- Aquaculture 2009 v.286 no.3-4 pp. 254-258
- Paralichthys olivaceus, flounder, marine fish, mortality, water temperature, fish diseases, viral diseases of animals and humans, Viral hemorrhagic septicemia virus, disease control, heat treatment, fish culture, mariculture, Japan
- Viral hemorrhagic septicemia virus (VHSV) infection has been one of the major obstacles for Japanese flounder Paralichthys olivaceus culture both in inland tank systems and open sea net-pens in Japan. The mortality due to the disease in cultured Japanese flounder occurs in the cold-water season at temperatures mostly below 15 °C. We examined the effect on the disease by shifting the rearing-water temperature to a higher temperature (20 °C) as a potential control measure. Japanese flounder reared in aquariums were infected with a VHSV isolate JF00Ehi1, and the water temperature was shifted from 14 °C to 20 °C (Experiment I) and from 20 °C to 15 °C (Experiment II). In Experiment I, earlier shifting resulted in lower cumulative mortality rates. In Experiment II, the group of fish reared for a longer period at 20 °C showed lower cumulative mortalities. In a third set of experiments, fish inoculated with the virus were reared at 20 °C or at 25 °C (a viral non-permissive temperature), observing no mortality in either group. Viral multiplication was detected at a low level in the fish at 20 °C but not in those at 25 °C. At 21 dpi, these fish were challenged with the virus and reared at 14 °C, yielding no mortality in the 20 °C group, and 92% in the 25 °C group. These results indicate that rearing at 20 °C reduced mortality in the Japanese flounder experimentally infected with VHSV, probably inducing protective immune response against subsequent infection.